The present invention relates generally to the field of radiography and, more particularly, to a marker of intermediate density and a method of radiographic examination using such a marker. The invention further relates to a system of radiographic markers for use in such a method.
To convey pertinent information on radiographic film, radiologists and technicians frequently use markers which absorb xrays and cast a shadow when placed within the xray exposure field. Such markers are positioned either directly on a patient undergoing radiographic examination or on the cassette holding the radiographic film.
For example, right and left markers are routinely used to designate the anatomical orientation of the patient or to identify a particular extremity being examined. Markers are also used in trauma cases to localize the trauma site by placing the marker on the skin surface at the appropriate location prior to x-ray exposure. Further, markers are often placed on the surface of the examination table or the film cassette, within the exposure field but outside the image of the patient, to define the patient's physical orientation in relationship to the xray beam or the film, i.e., erect, prone, supine or decubitus.
In the past, radiographic markers have been constructed of materials having a high atomic number such as, for example, lead, mercury, steel or heavy metal salts. When exposed to xrays, markers having such high density completely attenuate the xray beam and cast a distinct shadow that is readily apparent on the xray film. The disadvantage here is that any tissue detail that falls within the shadow of the marker will be completely obscured. Metallic markers also create problems when employed in computerized tomography (CT) applications. CT scanners, which typically operate in the range of 60 to 80 KV, cannot tolerate the presence of metallic objects in the radiographic field. Such dense objects cause streaking which degrades the radiographic image. This problem is made more acute by the fact that the marker must have sufficient surface area to be imaged in at least one section radiographed by the scanner. A metallic marker having the required surface area would completely disrupt the scanning apparatus.
Accordingly, it has been the practice of those skilled in the art of general radiography to place such markers on the patient or the radiographic film outside the area of clinical concern. This practice encourages increasing the size of the xray field to ensure that the image of an important marker appears on the film. Unfortunately, one result of such a practice is that the patient's body is exposed to potentially harmful radiation beyond the specific site being examined. In cases where a radiographic examination is conducted and the image of a marker is not clearly visible within the exposure field, the exam is often repeated to either enlarge the exposure field or to reposition the marker. Again, the unfortunate result is that the patient is exposed to greater dosage of potentially harmful radiation.
To precisely locate a tissue area of particular concern on the radiographic film following exposure, there are circumstances where a marker is placed on a patient and purposely imaged while overlying anatomical structures. In such a case, it is the usual practice of those skilled in the art to use a small, metal, spherical marker measuring no more than about 1 to 2 mm in diameter. While the shadow from such a small marker is less likely to obscure important tissue detail, the shadow may be mistaken for a physiological calcification or an opaque foreign body. Further, because such a marker is necessarily of small size with a correspondingly small shadow, there is an inherent difficulty in discerning variations in the size and shape of the marker's image on the film. Thus, the information that can be conveyed by markers of this type is limited.
Finally, markers comprising lead, mercury and other toxic heavy metals cannot be deposited in landfills or incinerated and thus present a potential environmental hazard if improperly disposed of. This problem is exacerbated by the fact that during radiographic examination procedures markers are often contaminated by body fluids. While contaminated markers can be sterilized, to save time and expense they are, more typically, discarded after only a single use.
It is therefore an object of the invention to provide a radiographic marker which may be placed on a tissue structure and imaged without obscuring underlying anatomical detail.
It is a further object of the invention to provide such marker which is constructed from non-toxic material.
It is a still further object of the invention to provide markers of this type in various sizes and shapes to convey pertinent information on radiographic film.
It is another object of the invention to provide a marker for use in CT applications which may be placed on a tissue structure and imaged without obscuring underlying anatomical detail.
It is yet another object of the invention to provide a method of radiographic examination using such markers.